A solar cell is a semiconductor device that can convert solar energy into electric energy, and under a light condition, the interior of the solar cell may generate a photo-generated current that can be outputted through an electrode. A negative electrode of a solar cell structure with p-silicon is usually located in the front surface of the cell while a positive electrode thereof is located in the back surface of the cell. When the light radiates, the radiation of a proper wave length leads to a hole-electron pair generated in the semiconductor. A potential difference on a P-N junction makes a hole and an electron move through the junction in an opposite direction, thus leading to the flow of current, which may transmit the electric energy to an external circuit. Currently, a commercialized crystalline silicon cell is still based on a conventional cell, having relatively simple technical process, low manufacture cost, and high cost performance, but the conventional cell has the following defects, which are mainly that ohmic contact is formed by directly printing the back electrode on a silicon wafer, and it is very easy for a silver electrode to form a metal defect in the silicon wafer, so that the electrode becomes a severe electric leakage area, which reduces the photovoltaic conversion efficiency of the solar cell; and the edge of the back electrode needs to be covered by an aluminum back surface field, which increases the width of the back electrode and the cost of the back electrode paste, and is adverse to the increase of the photoelectric conversion efficiency. In order to solve the defects generated by the manufacturing method and increase the photoelectric conversion efficiency of the silicon solar cell, the present invention provides an all-aluminum back surface field aluminum paste for a crystalline silicon solar cell and a preparation method thereof.
Chinese Patent application No. [201110208995.7] discloses a back surface field of a crystalline silicon cell and a printing technology thereof, wherein the technology mainly prints an aluminum back surface field on the back of the silicon wafer firstly, and then prints a back electrode, which can preferably solve the defects of the prior art and can increase the photoelectric conversion efficiency of the crystalline silicon cell. The patent mainly states the preparation technology of the all-aluminum back surface field, but does not describe the preparation methods of the all-aluminum back surface field aluminum paste for a crystalline silicon solar cell and the back electrode paste.
Chinese Patent [CN103151097A] discloses a preparation method of an all-aluminum back surface field paste for a crystalline silicon cell, and particularly, to a preparation method of an all-aluminum back surface field back electrode paste for a crystalline silicon cell. The paste is mainly added with a low melting cladding base metal, wherein a coating is tin or silver, and an object coated is one or several of base metals. The silver powder is enabled to form a good sintering interlay with the aluminum back surface field while improving the preparation technology of the back electrode, so that a dilatation coefficient is matched with the aluminum back surface field, the sintering interlay is not easy to crack and slab and has good electric conductivity, and the ohmic contact performance of the paste and the welding performance of a welding strip can be maximally guaranteed, so that the all-aluminum back surface field technology is completely performed. The patent mainly describes the improvement of the back electrode paste and the perfection of the technology thereof, but does not change the properties of the paste. Meanwhile, the back electrode paste has very high cost. Moreover, the adhering condition of the aluminum back surface field and the silver paste is not explained, which has essential difference with the changed aluminum paste provided by the present patent.
Chinese Patent [CN103746043A] discloses a preparation method of an all-aluminum doped solar cell, and more particularly, to a preparation method of an N-type solar cell. Firstly, an all-aluminum back surface field is prepared using a full back surface field screen printing plate not containing a back electrode figure and then is sintered under a high temperature to form a good P-N junction; and then the silver paste is sintered into the paste under a low temperature, and the back electrode is prepared through low temperature sintering, which overcomes the problem that the conventional silver aluminum paste back electrode can be only sintered under a high temperature. Because the sintering temperature of the back electrode is low, the sintering depth of the back electrode is less than the diffusion depth of the aluminum, which will not affect the quality of the P-N junction. The patent mainly describes a preparation method of an N-type all-aluminum back surface field for a solar cell. Compared with the conventional technology, the technology is added with a low temperature sintering technology, which has a conflict with a production line, and the patent does not describe a preparation method of a special silver and aluminum paste for an all-aluminum back surface field concretely. Similar patents also comprise [CN202996849U] and [CN102903765A].
Chinese Patent [CN103219062A] discloses a preparation method of a polymer thick film solder alloy conductor composition, which relates to a solder alloy powder that is composed of tin, silver, and copper with low melting point, and the prepared composition may be used to other applications that need electrical conductivity (low resistance). However, the composition is not applicable to the crystalline silicon solar cell.